Leandro Oriente

One battlestation, two computers

Sharing my desk between two Macs, with a USB switch and DDC to make the monitor follow.

Published in 3 minute read

A hand presses one switch to share a monitor, split keyboard, and mouse between a laptop and a small desktop computer.

I use a MacBook Pro for work, and I bought a CalDigit TS4 dock to connect everything on my desk. The peripherals, network, monitor, and power all reach the MacBook through a single Thunderbolt cable. When I need to take it out, I just unplug that one cable and leave the rest of the battlestation connected.

Before
Before: one MacBook Pro and one dock The MacBook Pro connects to the CalDigit TS4 with one Thunderbolt cable carrying power, data, and video. The dock connects to Ethernet, the monitor, keyboard, trackpad, webcam, microphone, speakers, and wired headphones. Before: one MacBook Pro and one dock The MacBook Pro connects to the CalDigit TS4 with one Thunderbolt cable carrying power, data, and video. The dock connects to Ethernet, the monitor, keyboard, trackpad, webcam, microphone, speakers, and wired headphones.

That worked well while I had one computer. After buying a Mac mini, I needed a way to use the same desk with both Macs.

I could move the Thunderbolt cable between them whenever I wanted to switch, but that kind of sucks.

Buying a second keyboard, mouse, webcam, and audio setup wouldn’t work. I have limited space on my desk, and I’m not willing to duplicate everything I have.

Moving the dock would also complicate my private VLAN and static-IP configuration, which I wanted to keep stable.

So I bought a USB switch to share the peripherals. Pressing its button moves the USB devices from one computer to the other, allowing me to switch without moving the dock’s Thunderbolt cable.

The monitor still needed a separate action. My MacBook connects to the monitor through DisplayPort, while the Mini uses HDMI 2. After switching the peripherals, I had to use the monitor’s controls to select the corresponding input.

After
After: two computers share one workstation The MacBook Pro connects to the CalDigit TS4 by Thunderbolt, which also supplies its power. The dock keeps its Ethernet connection and connects to the shared monitor through DisplayPort and to the USB switch. The Mac mini has its own power and Ethernet, and connects to the same monitor through HDMI 2 and to the same USB switch. The switch shares one keyboard, trackpad, webcam, microphone, speaker setup, and pair of wired headphones between both computers. After: two computers share one workstation The MacBook Pro connects to the CalDigit TS4 by Thunderbolt, which also supplies its power. The dock keeps its Ethernet connection and connects to the shared monitor through DisplayPort and to the USB switch. The Mac mini has its own power and Ethernet, and connects to the same monitor through HDMI 2 and to the same USB switch. The switch shares one keyboard, trackpad, webcam, microphone, speaker setup, and pair of wired headphones between both computers.

I already had to press the USB switch, so manually toggling the monitor looked quite dumb.

Making the monitor follow

The monitor supports DDC, short for Display Data Channel. Its command interface, DDC/CI, allows software to control supported monitor settings over the display connection. That includes selecting an input, which made this automation possible.

Both Macs already run BetterDisplay, which can send those input-selection commands. I just needed to know when to send them.

The USB switch doesn’t provide an interface to detect when I press its button. I had to detect the change myself. The obvious place to look was a USB device I’m unlikely to disconnect during normal use.

My keyboard provided that signal. When I press the switch, the keyboard disconnects from one Mac and appears on the other. Its arrival tells the receiving computer that the peripherals have moved to it.

I built a small Swift helper that runs on each Mac and listens for that connection event. After a brief delay to let the USB connection settle, it asks BetterDisplay to select that computer’s monitor input through DDC/CI.

The helper responds only to arrivals. Disconnections cancel pending actions, so unplugging a Mac doesn’t itself send an input-change command.

The helper runs automatically in the background. I added commands to Raycast, a macOS app launcher, so I could control it without opening a terminal. From there, I can enable or pause the automation, check its status, and test whether the keyboard is being detected.

Sleep and wake needed one more adjustment. I enabled automatic input selection on the monitor, so it changes inputs when a Mac wakes.

Now I can switch my entire workstation to a different computer with the touch of a button.

And nothing makes a lazy developer happier than spending a night fixing a problem that takes a second every day.